<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">

    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css" integrity="sha384-9aIt2nRpC12Uk9gS9baDl411NQApFmC26EwAOH8WgZl5MYYxFfc+NcPb1dKGj7Sk" crossorigin="anonymous">
 
    <title>Demo system</title>
  </head>
  <body>
    <nav class="navbar navbar-dark bg-dark">
      <a class="navbar-brand" href="#">
      Demo system
      </a>
    </nav>
    <div class="container" id="rrr"></div>
    <script src="bundle.js"></script>
    
  </body>
</html>